The invention relates to an apparatus for the exploration and recovery of petroleum and natural gas by the means of output wells. Especially the invention relates to a perforating gun as claimed in the preamble of patent claim 1. In particular with such apparatuses the recovery of petroleum and natural gas is possible by the means of so called fracking. Fracturing is a well-stimulation technique in which rock is fractured by a pressurized liquid. The process involves the high-pressure injection of a fracking fluid into a wellbore to create cracks in the deep-rock formations through which natural gas and petroleum will flow more freely. When the hydraulic pressure is removed from the well, small grains of hydraulic fracturing proppants (either sand or aluminum oxide) hold the fractures open. Therefore into the casing of a wellbore at least one perforating gun is placed and subsurface explosions are performed by the means of such a perforating gung. Such a perforating gun is disclosed in U.S. Pat. No. 8,794,326 B2 . The perforating gun comprising an outer tube which is designed as a tubular housing of the perforating gun having several recesses and an inner tube within the outer tube which is designed as a charge holder to hold a plurality of shape charges. Each recess is designed for corresponding to one shape charge so that after ignition and detonation of the shape charges a high pressure and high speed jet is generated and directed to the corresponding recess. These jets permeate the recesses of the outer tube and run into the layer of earth in radial direction of the perforating gun. Thereby on the one hand the outer tube has to withstand a large compression pressure, which is built up by the earth mass into depth where the perforation gun is placed. On the other hand the outer tube has to be free of deformation during and after the detonation of the shape charges to make it possible that the perforation gun can be removed from the casing of the wellbore.
US 2014 041 515 A1 and WO 2014 182 304 A1 disclose perforating guns as well, whereby the improvement of the design and the setting up of the recesses into the outer tube are discussed.
US 2002 189 483 A1 discloses the mechanical stress of the outer tube during the ignition of the shape charges of the perforation gun and during the expansion of the jets. Thereby the problem of the propagation of the shock waves into the outer tube of the perforation gun by impact of the jets onto the outer tube is discussed. Therefore an improvement of the design of the recesses of the outer tube is recommended to influence the expansion of the jets and the shock waves in a positive matter.